Investigators reveal what Florida suspect told them after allegedly killing 4, including mom holding her baby

Investigators say that when they captured Marine veteran Bryan Riley outside the Lakeland home where he allegedly killed a couple, their 3-month-old son and the boy's grandmother, he told them, "You know why I did this."

But they say they don't and, in fact, may never know why Riley launched an attack against a family he had no known connection with, except that he may have been mentally ill. Riley's girlfriend told investigators that he had been saying he could communicate directly with God. "The big question that all of us has is, 'Why?'" local prosecutor Brian Haas said after Sunday's slayings. "We will not know today or maybe ever."